1. Field of the Invention
This invention relates to an automated guided vehicle having an arm and a manipulator so as to transport and transfer a workpiece.
2. Background
In recent years, cassettes storing, for example, semiconductor wafers, are frequently transferred by an Automated Guided Vehicle (hereinafter referred to as an AGV) in a clean room for manufacturing semiconductor devices or FPDs (Flat Panel Displays) exemplified by LCDs (Liquid Crystal Displays).
At the present time, machines such as robots and human frequently and simultaneously perform operations at the same place in facilities for manufacturing semiconductor devices.
If AGVs for transporting wafer cassettes and human perform operations to be intermingled with each other, an issue of securing safety is raised due to the enlargement of size and weight of the wafer.
To improve safety of the AGV having manipulators for transferring wafer cassettes, for example, a protective fence, which is formed between the manipulator and the human, has been proposed.
FIG. 6 is a perspective view showing an example of the structure of a conventional AGV 100. Referring to FIG. 6, reference numeral 101 represents a vehicle portion having a control unit and wheels (not shown) and capable of moving in directions indicated with arrows A and A'.
A plurality of wafer cassette 102 can be mounted on an upper surface 101a of the vehicle portion 101. Moreover, an articulated manipulator 103 is mounted on the upper surface 101a.
Moreover, protective fences 104 are disposed on the upper surface 101a of the vehicle 101 to be located on end portions 101b-2 to 101b-4 except for an end portion 101b-1.
FIG. 7 is a perspective view showing the schematic structure of a clean room in which the AGV 100 shown in FIG. 6 are operated.
As shown in FIG. 7, a plurality of apparatuses 110-1, 110-2, . . . , (hereinafter expressed as 110-n if necessary) are disposed in the clean room.
The apparatuses 110-n each has a mounting portion 111. The wafer cassettes 102 are mounted on a specific surface of the mounting portion 111. However, the element 102 is not limited to the wafer cassette and, therefore, it may be a semiconductor wafer or a box in which the semiconductor wafers are stored.
In the foregoing clean room, the AGV 100 moves along surfaces of the apparatuses 110-n having the mounting portions 111. The apparatuses are usually disposed on opposite sides of the movement passage. The AGV cannot always move on the same side of the apparatuses.
However, the manipulator 103 is able to perform the transferring operation at only end portion 101b-1 of the upper surface 101a of the AGV 100 at which the protective fence 104 is not provided. Therefore, the end portion 101b-1 of the upper surface 101a of the AGV 100 needs to always face each apparatus 110-n.
Therefore, there is a case that the AGV 100 needs to perform a spin turn as indicated by B-2 at position B in FIG. 7. Since the movement of the AGV 100 must temporarily be interrupted when the spin turn is performed, the transferring operation speed cannot be raised.
In general, there is a case that semiconductor wafers are handled in a small clean room. However, since the above-mentioned operation of the AGV 100 requires a large space for the movement thereof, it may cause an excessive waste of time.
Another conventional art will now be described with reference to FIGS. 10 to 11.
FIG. 10 is a perspective view showing a state in a clean room of OHT (Overhead Hoist Transportation) type with which wafers are suspended from upper position. Such clean room has been recently employed.
Since semiconductor wafers, which are manufactured in a clean room, have been enlarged in recent years, a method called "ME" (Mini-Environment) with which wafers are stored in each box has been employed. Since wafers are stored in boxes provided for the AGV, contamination with dust can be prevented. In view of transportation of wafer cassette under such ME, the clean room of OHT type in which wafers are suspended from the ceiling has been employed in order to effectively use the space of the clean room.
As shown in FIG. 10, the clean room of the OHT type differs from the clean room shown in FIG. 7, and requires an opened space above the position of each apparatus 420 at which the wafer cassette is mounted.
It leads to a fact that each apparatus 420 or a stocker 420a having a load port 421 forwardly projecting is usually employed.
FIG. 11 is a perspective view showing the relationship between the apparatuses 420 from which the load ports 421 are projected and an AGV 400a in a case where the OHT type structure is employed.
According to the structure as shown in FIG. 11, since the load ports 421 project over the front surfaces of the apparatuses 420, spaces are created between a certain load port 421 and an adjacent load port 421.
Since a human may exist in the above-mentioned space as shown in FIG. 11, there is a possibility that the arm 403 and the human being come in contact with each other during the transferring operation. Therefore, in view of the case as shown in FIG. 11, even if a protective fence is provided on the AGV, a defense device is required between each apparatus and the AGV for safety.